Many portable devices, for example mobile telephones, are equipped with a display such as a glass or plastic display window for providing information to the user. Furthermore such display windows are now commonly used as touch sensitive inputs. The use of a touch sensitive input with the display has the advantage over a mechanical keypad in that the display may be configured to show a range of different inputs depending on the operating mode of the device. For example, in a first mode of operation the display may be enabled to enter a phone number by displaying a simple numeric keypad arrangement and in a second mode the display may be enabled for text input by displaying an alphanumeric display configuration such as a simulated Qwerty keyboard display arrangement.
However such touchscreen inputs have a disadvantage with respect to mechanical keys in that the user does not experience the usual expected click or mechanical switch feedback to indicate that an input has been detected.
To attempt to overcome this some equipment has been provided with a mechanical or audible simulation of a key press.
This feedback is known as haptic feedback when felt. Some touch screen devices have been equipped with device haptic feedback, in other words an ordinary vibration such as produced by the speaker within the device is used to make the whole device shake (and also provide an audio cue of the key press) as the user touches the screen and is detected. In other devices an eccentric mass is used to vibrate the devices when the device detects that a user has touched the screen. These device-haptic devices however are themselves problematic as they require significant current to operate in order to generate significant feedback force. This is generally because the construction of the device often requires that the front window is firmly located or fixed to the surrounding frame or connected in such a way to significantly damp the force generated by the actuator before it is applied.
For example a front window part of the display, touch interface and foam gasket can be firmly or rigidly connected to the frame by a clip which is fixed by adhesive to the frame. Similarly the front window part of the display and touch interface can be located with respect to the case by the foam gasket and clip. In order to prevent dust and other material from entering the delicate internal circuitry and mechanical parts of the device the foam gasket can be arranged to seal any gap between the case and the front window/touch sensor. These foam gaskets have the effect of assisting the rigid locating of the sensor and front window (especially under pressure) and can require significant current to be applied to the actuator in order to generate a feedback force detectable by the user. The foam gaskets are furthermore very sensitive in mechanical tolerances and during compression create an additional force which works against the actuator feedback force.
Furthermore such devices typically also use electro-acoustic transducers to produce audio for earpiece and integrated hands free (IHF) operations as well as for alert tones. The moving coil dynamic speaker configuration used is typically relatively large in relation to the volume within the device and require specific signal processing considerations in order that the acoustic frequency response is acceptable. Furthermore moving coil transducers can attract contaminants such as small iron particles from within the internal volume of the device and also through ports provided to enable acoustic wave transmission from the speaker to the external environment. These contaminants can cause distortion and faults within the speakers significantly reducing the lifetime of the device.
This application proceeds from the consideration that the provision of a flexible membrane connecting a display to the cover or main body of the device and capable of transferring the force provided by an actuator to the user by flexing and not significantly damping the force may provide both the physical and mechanical support for the display without unduly limiting the action of the display in producing tactile or haptic feedback and audio speaker functionality.
It is an aim of at least some embodiments of the invention to address one or more of these problems.